Bump gson from 2.5 to 2.8.5

[dependabot-preview]

Bumps gson from 2.5 to 2.8.5.

Changelog

Sourced from gson's changelog.

Version 2.8.5

2018-05-21 GitHub Diff

• Print Gson version while throwing AssertionError and IllegalArgumentException
• Moved utils.VersionUtils class to internal.JavaVersion. This is a potential backward incompatible change from 2.8.4
• Fixed issue google/gson#1310 by supporting Debian Java 9

Version 2.8.4

2018-05-01 GitHub Diff

• Added a new FieldNamingPolicy, LOWER_CASE_WITH_DOTS that mapps JSON name someFieldName to some.field.name
• Fixed issue google/gson#1305 by removing compile/runtime dependency on sun.misc.Unsafe

Version 2.8.3

2018-04-27 GitHub Diff

• Added a new API, GsonBuilder.newBuilder() that clones the current builder
• Preserving DateFormatter behavior on JDK 9
• Numerous other bugfixes

Version 2.8.2

2017-09-19 GitHub Diff

• Introduced a new API, JsonElement.deepCopy()
• Numerous other bugfixes

Version 2.8.1

2017-05-30 GitHub Diff

• New: JsonObject.keySet()
• @JsonAdapter annotation can now use JsonSerializer and JsonDeserializer as well.

Version 2.8

2016-10-26 GitHub Diff

• New: TypeToken.getParameterized() and TypeToken.getArray() make it easier to
  register or look up a TypeAdapter.
• New: @JsonAdapter(nullSafe=true) to specify that a custom type adapter handles null.

Version 2.7

2016-06-14 GitHub Diff

• Added support for JsonSerializer/JsonDeserializer in @​JsonAdapter annotation
• Exposing Gson properties excluder(), fieldNamingStrategy(), serializeNulls(), htmlSafe()
• Added JsonObject.size() method
• Added JsonWriter.value(Boolean value) method
• Using ArrayDeque, ConcurrentHashMap, and other JDK 1.6 features
• Better error reporting
• Plenty of other bug fixes

Version 2.6.2

2016-02-26 GitHub Diff

• Fixed an NPE bug with @​JsonAdapter annotation
• Added back OSGI manifest
• Some documentation typo fixes

Version 2.6.1

... (truncated)

Commits

• f649e05 [maven-release-plugin] prepare release gson-parent-2.8.5
• 4c685b2 Private constructor (#1324)
• d84e26d Issue 1242: Printing Gson version when throwing AssertionError and IllegalArg...
• 1215841 Merge pull request #1281 from greatjack1/master
• 3547420 Merge branch 'master' into master
• a6890bb Fixed google/gson#1310 (#1311)
• 57085d6 2.8.4 README
• f2dd56d 2.8.4 changelog
• f77615e 2.8.4
• d8857cd updated release process to the current steps
• Additional commits viewable in compare view

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[sladyn98]

This https://github.com/google/gson/blob/master/CHANGELOG.md does not seem to suggest it would break anything in our build. It could be merged successfully.
cc @timja @Casz @oleg-nenashev